[Show abstract][Hide abstract] ABSTRACT: Herein, we explore the immobilization of nickel on various carbon supports and their application as electrocatalysts for the oxidation of propargyl alcohol in alkaline medium. In comparison with massive and nanoparticulated nickel electrode systems, Ni-doped nanoporous carbons provided similar propargyl alcohol conversions for very low metallic contents. Nanoparticulated Ni on various carbon supports gave rise to the highest electrocatalytic activity in terms of product selectivity, with a clear dependence on Ni content. The results point to the importance of controlling the dispersion of the Ni phase within the carbon matrix for a full exploitation of the electroactive area of the metal. Additionally, a change in the mechanism of the propargyl alcohol electrooxidation was noted, which seems to be related to the physicochemical properties of the carbon support as well. Thus, the stereoselectivity of the electrooxidative reaction can be controlled by the active nickel content immobilized on the anode, with a preferential oxidation to (Z)-3-(2-propynoxy)-2-propenoic acid with high Ni-loading, and to propiolic acid with low loading of active Ni sites. Moreover, the formation of (E)-3-(2-propynoxy)-2-propenoic acid was discriminatory irrespective of the experimental conditions and Ni loadings on the carbon matrixes.
[Show abstract][Hide abstract] ABSTRACT: The direct electron transfer of cytochrome c has been studied at screen-printed graphite macroelectrodes without recourse to mediators or the need for any electrode pre-treatment as is commonly employed within the literature. A wide range of pH values from 2.0 to 11.0 have been explored upon the electrochemical response of cytochrome c and different voltammetric signatures have been observed. The direct electron transfer of the alkaline transition of cytochrome c was found impeded within alkaline media leading to either an irreversible redox process or even no voltammetric responses. In acidic aqueous media the electrochemical process is observed to undergo a mixed diffusion and adsorption controlled process rather than a purely diffusional process of the native conformation as observed at pH 7.0. Interestingly, at pH 3.5 a new conformational state is revealed in cooperation with the native conformation. The immobilization of the protein was satisfactorily obtained using a simple method by cycling the protein at specific solution pH values allowing amperometric responses to be obtained and gives rise to useful pseudo-peroxidase activity for sensing H2O2. Apparent Michaelis-Menten constant values (Km) were calculated via the Lineweaver-Burk method with deduced values of 25 ± 4, 98 ± 12 and 230 ± 30 mM, respectively for pH values of 2.0, 3.0 and 7.0. Such work is important for those utilising cytochrome c in bio-electrochemical and related applications.
[Show abstract][Hide abstract] ABSTRACT: Food industries such as almond industry generate large volumes of wastewater in their processes and common techniques are not always efficient for treating this kind of effluents. In this work, the feasibility of a treatment for pollutants removal of a real industrial wastewater by electrochemical oxidations studied at laboratory scale and then scaled-up to pre-industrial scale. The first stage of the work was performed at laboratory scale, using a 63 cm2 cell, where different anodes (Ti/Pt, and DSA anodes (Ti/RuO2 and Ti/IrO2)) and the optimal experimental conditions (pH, current density, temperature and [Cl−]) were studied and established. By using a DSA-Cl2 anode (Ti/RuO2), pH 9, j = 50 mA cm−2, [Cl−] = 2000 mg L−1 and room temperature, chemical oxygen demand (COD) was removed up to 75% and results show that electrooxidation can remove organic pollutants.
In the second stage the scaling-up of the process from laboratory to pre-industrial scale was performed, by using a 3300 cm2 cell. The electrochemical reactor was finally powered by a photovoltaic generator directly connected, in order to operate by using a renewable energy and a COD elimination of 80% was achieved.
Separation and Purification Technology 02/2014; 123:15–22. · 2.89 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitration in proteins is a physiologically relevant process and the formation of 3-nitrotyrosine was first proposed as an in vivo marker of the production of reactive nitrogen species in oxidative stress. No studies have been published on structural changes associated with nitration of myoglobin. To address this deficiency the electrochemical nitration of equine skeletal muscle (Mb) at amino acid tyrosine 103 has been investigated for the evaluation and characterization of structural and thermal stability changes. Y103 in Mb is one of the most exposed tyrosine residues and it is also close to the heme group. Effects of Y103 nitration on the secondary and tertiary structure Y103 have been studied by UV-Vis, circular dichroism, fluorescence and NMR spectroscopy and by electrochemical studies. At physiological pH, subtle changes were observed involving slight loosening of the tertiary structure and conformational exchange processes. Thermal stability of the nitrated protein was found to be reduced by 5 °C for the nitrated Mb compared with the native Mb at physiological pH. Altogether, NMR data indicates that nitrated Mb has a very similar tertiary structure to that of native Mb, although with a slightly open conformation.
Archives of Biochemistry and Biophysics 11/2012; · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Screen printed graphite electrodes (SPGEs) have been characterized in the room temperature ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6] by studying pertinent electrochemical parameters of the electroactive species ferrocene (Fc), 1,4-benzoquinone (BQ), 1,4-diphenyl-9,10-anthraquinone (AQ), tetracyclone (TC) and benzophenone-3 (BZ-3). Diffusion coefficients and kinetics calculations together with Digisim simulations for comparison were performed. Additionally, the reductive cyclovoltammograms of organic carbonyl containing BQ, AQ, TC and BZ-3 derivatives provided valuable information and comparison of the electrochemical reduction of the CO functional group in model molecules of different size, solubility and π-aryl aromaticity. Finally, potentialities for the electroanalytical measurement of BZ-3 at SPGEs via the room temperature ionic liquid [C6MIM][PF6] have been evaluated.
[Show abstract][Hide abstract] ABSTRACT: The electrooxidation of the unsaturated propargyl alcohol has been explored on NiOOH electrodes in alkaline solution. Cyclic voltammetry, chronoamperometry and electrolyses were performed for the electrochemical response of propargyl alcohol. The identification and quantification of the final products from the electrolyses have been carried out. No evidence for the formation of propiolic acid has been found, however, a new product, (Z)-3-(2-propynoxy)-2-propenoic acid, was obtained. The stereochemistry of the product could be ascertained by 1H NMR spectroscopy. A tentative mechanism for the formation of (Z)-3-(2-propynoxy)-2-propenoic acid has been developed.
[Show abstract][Hide abstract] ABSTRACT: Bismuth-modified Pt nanoparticles supported on carbon have been employed as anode electrocatalyst for a direct formic acid fuel cell (DFAFC). Two different types of electrodes were used: a thin layer Pt/C working electrode deposited on a gold substrate and a coated catalyst (Pt/C) membrane. Bismuth was deposited on the Pt nanoparticles by irreversible adatom adsorption from a Bi3+ solution. Bi-modified thin-film working electrodes with different catalyst loadings (0.1, 0.5 and 1.0 mgPt cm−2) were tested for the electrooxidation of formic acid (2, 4.75 and 9 M formic acid solutions). Likewise, a Bi-modified coated catalyst membrane was used as anode in an air-breathing direct formic acid fuel cell. For this cell, polarization curves were obtained for different formic acid solutions. Independently of the type of electrodes, the presence of Bi caused a four/six fold increase of the electrooxidation currents as compared to unmodified Pt electrodes. Thus, the use of bismuth-modified carbon supported Pt nanoparticles is presented as an easy, feasible and versatile alternative for improving the efficiency of DFAFCs.
[Show abstract][Hide abstract] ABSTRACT: Platinum single crystal electrodes, Pt(h k l), represent ideal materials where studying surface sensitive reactions such as oxygen reduction reaction (ORR). Moreover, there is a great interest in testing carbon supported electrocatalyts mixed with Nafion (R) ionomer in order to directly evaluate catalysts under practical fuel cell conditions. Thus, we provide a first imaging attempt by scanning electrochemical microscopy (SECM) to locally evaluate the electrocatalytic activity during ORR on a Pt(1 1 1) single crystal electrode decorated with spots of commercial carbon supported platinum nanoparticles entrapped in Nafion (R). Both electrocatalysts present the same chemical composition and then, total surface area, particle size and crystallographic orientation at the electrode surface are the effects studied. Our SECM images prove that the peroxide pathway can also be considered a relevant reaction route on platinum electrodes. We agree with some recent reports pointing the Nafion (R) content and the three-dimensional surface electrode area as key factors to control for achieving a proper evaluation of the apparent number of electrons exchanged during ORR. (C) 2011 Elsevier Ltd. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: The direct electrochemical oxidation of methionine has been achieved at bare carbon based electrodes and for the first time at screen printed graphite electrodes in aqueous solutions. Due to scales of economy and intended use as a potential point-of-care sensor, the quantification of methionine was explored at screen printed electrodes, allowing linear ranges over the range 0.05–5.0 mM with a detection limit of 95 × 10−6 mol L−1 possible in model solutions. Application of this sensor was used for the determination of methionine in a pharmaceutical product containing a complex mixture of vitamins, amino acids, chelated minerals and additional factors with the results agreeing with manufacturers’ specification suggesting that this sensing platform holds promise as a rapid, sensitive and disposable sensor for methionine determination.
Sensors and Actuators B: Chemical. 07/2011; 155(2):831–836.
[Show abstract][Hide abstract] ABSTRACT: This work was carried out to study the treatment of almond industry wastewater by the electrocoagulation process. First of all, laboratory scale experiments were conducted in order to determine the effects of relevant wastewater characteristics such as conductivity and pH, as well as the process variables such as anode material, current density and operating time on the removal efficiencies of the total organic carbon (TOC) and the most representative analytical parameters. Next, the wastewater treatment process was scaled up to pre-industrial size using the best experimental conditions and parameters obtained at laboratory scale. Finally, economic parameters such as chemicals, energy consumption and sludge generation have been discussed.
[Show abstract][Hide abstract] ABSTRACT: We report the direct electrochemistry of cytochrome c at screen printed graphite electrodes which exhibits quasi-reversible voltammetric responses without the need for any chemical or electrochemical pre-treatment, use of mediators or nanomaterials. Through voltammetric studies and X-ray photoelectron spectroscopy (XPS) it is shown that carbonyl and carboxylic surface oxygenated species likely residing at edge plane like- sites/defects of the graphite comprising the screen printed electrodes are responsible for the favourable interaction of the cytochrome c with that of the screen printed electrochemical sensing platform.
The Analyst 04/2011; 136(10):2146-50. · 4.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The application of shape-controlled Pt nanoparticles is rapidly increasing mainly because surface reactivity is, for many cases, structure sensitive. Shape control is generally obtained by using capping agents which finally cover the surface. However, for many applications these adsorbed molecules have to be effectively removed. For this purpose UV/ozone has been recently proposed. However, although this methodology was shown to be effective for cleaning, its effects over the catalyst surface structure are still unclear. In this paper the effect of UV/ozone cleaning treatment on uncapped/clean shaped-controlled Pt nanoparticles is evaluated. The results demonstrate that this procedure strongly perturbs the surface structure of the nanoparticles, significantly modifying their catalytic properties, but without altering their size and shape.
[Show abstract][Hide abstract] ABSTRACT: Electrochemical technologies have proved to be useful for the treatment of wastewater, but to enhance their green characteristics it seems interesting to use a green electric energy such as that provided by photovoltaic (PV) cells, which are actually under active research to decrease the economic cost of solar kW. The aim of this work is to demonstrate the feasibility and utility of using an electrooxidation system directly powered by a photovoltaic array for the treatment of a wastewater. The experimental system used was an industrial electrochemical filter press reactor and a 40-module PV array. The influence on the degradation of a dye-containing solution (Remazol RB 133) of different experimental parameters such as the PV array and electrochemical reactor configurations has been studied. It has been demonstrated that the electrical configuration of the PV array has a strong influence on the optimal use of the electric energy generated. The optimum PV array configuration changes with the intensity of the solar irradiation, the conductivity of the solution, and the concentration of pollutant in the wastewater. A useful and effective methodology to adjust the EO-PV system operation conditions to the wastewater treatment is proposed.
Environmental Science and Technology 07/2010; 44(13):5182-7. · 5.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The structure sensitive catalytic activity for oxygen reduction reaction (ORR) on shape-controlled Pt nanoparticles (NPs) is directly imaged using scanning electrochemical microscopy (SECM). We synthesize and compare four types of Pt NPs: spherical, cubic, hexagonal, and tetrahedral-octahedral. Our SECM images show the hexagonal Pt NPs displaying the highest activity for ORR in two acid electrolytes. Meanwhile, cubic and tetrahedral-octahedral NPs drastically change their activity depending on specific adsorption of the different anions in solution. The NPs morphology produces predominant crystallographic planes at the surface of these shape-controlled Pt NPs, which are responsible for their different catalytic activity. Our results translate the studies on Pt single crystal electrodes present in the literature into Pt NPs that are useful as a catalyst in real fuel cells.
Journal of the American Chemical Society 04/2010; 132(16):5622-4. · 10.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The electrosynthesis of N-acetyl-l-cysteine (NAC) from the electroreduction of N,N-diacetyl-l-cystine (NNDAC) using a Polymer Electrolyte Membrane Electrochemical Reactor (PEMER) has been carried out. The Membrane Electrode Assembly (MEA) was formed by a cathode with a catalyst layer made of Pb/C 20 wt% supported on Toray Paper and a catalyst loading of 0.5 mg Pb cm−2. The anode was a 2 mg Pt cm−2 gas diffusion anode fed with H2. The main advantages of this process are: (1) the electrochemical reactor allows to carry out the electrosynthesis without supporting electrolyte, improving in this way the NAC purification and (2) a pronounced decrease of the electrosynthesis energy consumption due to both, the small internal resistance of the PEMER (electrode gap very small and electrolyte very conductive) and the choice of the H2 oxidation as anodic reaction in stead of the oxygen evolution reaction from water oxidation. The large number of pharmaceutical applications of NAC, as well as the high versatility of the PEMER for electrosynthesis processes, makes interesting the use of MEAs for electroorganic synthesis.
[Show abstract][Hide abstract] ABSTRACT: The electrocatalytic activity for the oxygen reduction reaction (ORR) of different shape-controlled gold nanoparticles (NPs) and nanorods has been studied by scanning electrochemical microscopy (SECM) TEM images and lead underpotential deposition (UPD) voltammetric profiles were used to physically and electrochemically characterize all gold particles studied here providing information on the shape and surface structure of the different NPs and nanorods The SECM results demonstrate that cubic gold NPs are the most active towards ORR in 0 1 M NaOH followed by the spherical gold NPs and finally by the short gold nanorods These results are in agreement with previous studies using conventional electrochemical techniques with gold NPs and single crystal electrodes since they established that higher ratio of (1 0 0) domains provide higher catalytic activity for ORR (C) 2010 Elsevier Ltd All rights reserved